Road safety barrier

ABSTRACT

A road safety barrier ( 1 ) comprises a series of beam sections ( 2   a  to  2   d ) together forming a length of barrier and supported above the ground by way of posts ( 3   a  to  3   g ). The positions of successive posts along at least part of the length of the barrier shift relative to the centres of the beam sections (C). The shift may be progressive but uniform along a section thereof so that the flexibility of the barrier is substantially constant. Shifting the locations of the posts along the length of the barrier by an increasing or decreasing amount has the effect of increasing or decreasing the strength of the barrier so that different road conditions can be accommodated even though beam sections of constant length are used to construct the barrier.

The invention relates to road safety barriers and in particular but notexclusively to road safety barriers of the ‘W’ profile ‘post and beam’type.

One known road safety barrier comprises a series of ‘W’ profile beamsections that are joined together at overlapping ends. The beams aresupported above the ground by posts positioned along the length of thebarrier. The design criteria for a given length of safety barrier withrespect to impact resistance and flexibility on impact are determinedaccording to the road conditions. For example, the safety barrier of acentral reservation between roads carrying vehicles travelling inopposite directions may be designed to offer a relatively highresistance with lower flexing on impact in order to ensure errantvehicles are deflected back into their direction of travel. On the otherhand, a more flexible barrier may be desirable in other circumstances,not least because it may be simpler and less expensive to install.

The impact response, particularly with respect to flexibility, of asafety barrier of this type is governed to a significant extent by thelength of beam sections and number of posts per section. Essentially,since the beam sections are manufactured in standard lengths, the moreposts supporting each section, the more resistant the barrier is toflexing on impact. In these ‘post and beam’ prior art road safetybarriers, the posts are invariably positioned at the same locationsrelative to each beam section. That is to say, for any given length ofbarrier, the posts are positioned at points which are the same distancefrom the position where beam sections overlap. In another configuration,representing a barrier more resistant to flexing on impact, two postsper section may be adopted, positioned at the same location relative tothe section supported by them from one beam section to the next.

Installation of these ‘post and beam’ road safety barriers requirescareful planning in order that the lengths of beam sections and numberof posts carried to the site are appropriate to meet the impact designcriteria for the section of safety fence under construction. This islimiting in cases where the crash characteristics of the barrier may beredesigned or varied during the installation programme. The fixedpost-beam relationship for the length of the barrier also makes itdifficult to construct a barrier that has an impact flexibility thatvaries along its length to provide for changing road conditions. Forexample, it may be necessary to construct a stretch of barrier alongsidea bridge buttress having a different flexing characteristic from thesections of barrier farther away. In this case, different post positionswill be required. A further limitation arises if the design criteriarequire a gradual or even a stepped change in barrier flexibility over agiven stretch of road.

For example, a known barrier comprises a series of beam standard lengthsections of 3.2 m, with posts spaced either at intervals of 1.6 m or 3.2m. In the first case, each post is positioned 0.8 m from the centralpoint of overlap of sections or, for a less flexible barrier in thesecond case, an additional post is provided midway between the posts ofthe first case so that there are two posts supporting each section. Thebeam is provided with means for facilitating attachment of posts at eachof these positions. The posts may be fixed to the beam section by meansof bolts passing through slots or holes in the section. However, theproblem is that as the slots or holes are formed during the manufactureof the beam section, the ability to add additional ones to a given beamsection on site in order to provide a stiffer section of barrier islimited. It is therefore not possible to construct a barrier withflexibility characteristics that differ from either the 1.6 m-spacingbarrier, or the 3.2 m spacing barrier.

It is an aim of the present invention to provide a road safety barrierthat alleviates the aforementioned problems and limitations.

According to the present invention, there is provided a road safetybarrier comprising a series of beam sections together forming a lengthof barrier and supported above the ground by way of posts, wherein thepositions of successive posts along at least part of the length of thebarrier shift relative to the centres of the beam sections.

In a preferred embodiment, the shift may be progressive but uniformalong a section thereof so that the flexibility of the barrier issubstantially constant. A change in the degree of shift from one post tothe next can provide for a change in the flexibility of the barrier fromone section thereof to another. The ability to shift the post positionsalong the length of the barrier allows the designer to tailor or varythe flexibility of the barrier along a predetermined length thereofusing beam sections of substantially equal length. This allows greaterflexibility in the use of standard length beam sections by simplifyinginstallation time and costs. Furthermore, since the design criteria aredetermined by the performance classes of the relevant national orinternational standards (e.g. European Standard EN1317 Part 2), it isadvantageous to have a system in which the flexibility/stiffness of thebarrier can be altered according to the constraints of those officialstandards, whilst keeping the installation time and costs to a minimum.For example, a crash test scenario could involve use of a barrier havinga post spacing that progressively changes along its length and so has acrash characteristic (i.e. stiffness) which progressively changes. Thismakes it easier to determine whether a given post spacing/barrierstiffness meets a performance class.

Fixing means are provided on the beam sections to facilitate fixing ofthe posts to the beam. In accordance with a preferred embodiment, theseare provided at more than two but preferably more than five locationsadvantageously equi-spaced along the longitudinal axis of the beam. Theprovision of a greater number of fixing means permits shifting of postsfrom one to the next by smaller increments. This makes it easier toinstall a barrier which meets a given performance class using beamsections of the same length.

The advantage arising from the present invention is that by increasingthe number of fixing means along the length of a beam section, theoptions for varying the positional relationship between adjacent postsincreases. It is no longer necessary to position posts symmetricallywith respect to the beam sections. Shifting the locations of the postsalong the length of the barrier by an increasing or decreasing amounthas the effect of increasing or decreasing the strength of the barrierso that different road conditions can be accommodated even though beamsections of constant length are used to construct the barrier. A stretchof barrier of constant strength along its length is established bylocating the posts at an even spacing relative to one another, but thedesign options in terms of the absolute strength of the barrier for agiven beam section length are increased.

According to the present invention, there is further provided a methodof constructing a road safety barrier which at least in part comprises aseries of beam sections of substantially equal length supported abovethe ground by posts, the method comprising shifting the locations of theposts relative to the centres of the beam sections from one beam sectionto the next.

This method is particularly advantageous as it allows thestrength/flexibility of the barrier to be varied in accordance with theobstacles or features such as bridge buttresses that are situated alongthe length of the barrier as the barrier is constructed using a standarduniform length than necessary in the prior art method of construction.

Advantageously, the number of posts required that will allow the barrierto conform to the necessary safety criteria can be kept to a minimum,thereby minimising the cost of the barrier itself, and the associatedinstallation and maintenance costs.

In some embodiments of the invention, the separation between adjacentposts may be such that some beam sections are not directly supported byposts, but are instead supported by the beams (and their supportingposts) to which they are joined at either end.

According to the present invention, there is further provided a methodof testing a crash barrier system, the system comprising a series ofbeam sections together forming a length of barrier and supported abovethe ground by way of posts, wherein the positions of successive postsalong at least part of the length of the barrier shift relative to thecentres of the beam sections such that the stiffness of the barriervaries along the length, the method comprising conducting road crashtests at differing points along the length and determining whether theresults of said crash tests satisfy predetermined criteria.

An embodiment of the invention will now be described by way of examplewith reference to the following drawings, in which:

FIG. 1 depicts a length of road safety barrier constructed in accordancewith the prior art;

FIG. 2 a shows a beam section which may be used to form part of thebarrier according to the invention;

FIG. 2 b is a cross-sectional view of the beam section of FIG. 2;

FIG. 3 is a cross-sectional view of a ‘Z’ section post which may be usedto support the barrier according to the invention; and

FIGS. 4-7 are simplified representations of barriers according toexemplary embodiments of the invention.

FIG. 1 illustrates a prior art ‘post and beam’ type road safety barrier1 constructed from beam sections 2 a to 2 d of length ‘L’ supportedabove the ground by a series of posts 3 a to 3 g. The beam sections 2 ato 2 d are joined and secured together by bolts (not shown) passingthrough apertures 4 a to 4 c and/or 7 a to 7 d provided at overlappingends of adjacent beam sections such that the distance between thecentres of adjacent beam sections is ‘C’. Apertures 5 a to 5 c and 6 ato 6 c are provided along the longitudinal axis of each beam section toprovide a fixing location for a supporting post. In this example, theposts 3 a and 3 b are fixed to apertures 5 a and 5 b respectively bybolts (not shown) and the same corresponding positions for the otherbeams along the length of the barrier 1. The posts are spaced by adistance ‘d’ inwardly with respect to the centre of respectiveoverlapping ends. It is apparent from FIG. 1 that the prior art barrieris supported by posts that are in a fixed positional relationship withreference to the centres of the beam sections.

FIG. 2 a shows a beam section 10 which may be used in accordance withone embodiment of the present invention. As illustrated in FIG. 2 b, thebeam section 10 has a ‘W’ profile. The section 10 is provided with aseries of fixing means in the form of slots indicated in FIG. 2 a by‘Slots A1, A2, A3; Slots B1, B2, B3, B4; and Slots C1 and C2′. Slots A1,A2 and A3 correspond to apertures 4 a, 4 b and 5 b of FIG. 1, slots A1and A3 providing for bolts to secure adjacent beam sections with anoptional post. Slots C1 and C2 correspond to apertures 3 a and 3 b ofFIG. 1 and provide fixing locations for posts. However, in contrast toFIG. 1, the beam section 10 is provided with additional fixing meansSlot B1, B2, B3 and B4 as shown substantially equi-spaced in relation tothe others. These additional slots, although is would be apparent to theskilled man in the art that an alternative form of post fixing means maybe adopted, provide fixing locations which allows the post locations tobe shift along the length of the barrier. Still further slots or fixingmeans may be provided in the beam section thereby allowing the posts toshift in relation to the beam sections by smaller increments along thelength thereof.

FIG. 3 is an example of a ‘Z’ section post 3 a which may be used inembodiments of the invention, showing additionally the orientationthereof in relation to the direction of traffic flow when installed.

FIG. 4 shows elevational and plan views of a longer section of roadsafety barrier 20 in order to illustrate the shift of posts relative tothe centres of the beam sections as the barrier advances from onedirection to the other. In this example, the barrier is constructed frombeam sections 22 a, 22 b, 22 c etc. which are of substantially equallength (3.2 m) and supported by posts 24 a, 24 b, 24 c etc which,although they are equally spaced apart (2 m), are staggered relative tothe centres or ends of the beam sections. In other words, in thisexample, the spacing of the posts is such that although post 24 g isfixed at the overlapping portions of adjacent beam sections 22 d and 22e respectively, the next recurrence of coincidence between a post andbeam section overlap occurs five beam section lengths away in eitherdirection. The frequency of coincidence is therefore a function of theaverage number of posts supporting each beam section, i.e. 1.6 (8 postsdivided by 5 beam sections) and so a function of the strength orflexibility of the barrier. Clearly, the closer the post spacing for agiven beam section length, the stronger the barrier because, on average,each beam section is supported by more posts. However, from theconstructional standpoint, it is clear that the flexibility or strengthof the barrier can be simply varied by varying the post spacing in aprogressive manner along the length thereof. Should it be desired toinstall a stronger section of barrier to shield a bridge buttress forexample, the contractor simply has to bring the spacing of the postscloser together for that section. The advantage with the barrierembodying the present invention is that he may do so using standard beamsections. It is also possible for a designer/contractor to change thestrength of a barrier after initial installation by shifting the postswithout need to change the beam sections as well.

FIGS. 5-7 show three alternative embodiments. In FIG. 5, there are 4posts supporting 3 beam sections—a ratio of 1.33 posts per section. InFIG. 6, the barrier is more flexible because there are fewer posts perbeam section on average, namely 8 posts supporting 9 beam lengths. InFIG. 7, 4 posts support 5 beam sections so that every 5 beam lengths (or‘repeat’), one beam is supported only by its adjacent beams.

Examples of the ratio, for a given length of barrier, of the distancebetween adjacent posts to the beam section length may include any oneof: 0.5; 0.625; 0.75; 0.875; 1.0; 1.125; and 1.25 although the moreflexibility there is for locating posts along a beam section, the morefinely graded the shifting of the posts may be.

Although the aforementioned examples show equal post spacing, the degreeof shift may increase or decrease along the length of the barrier tofacilitate a graded change in flexibility.

1. A road safety barrier comprising a series of beam sections togetherforming a length of barrier and supported above the ground by way ofposts, wherein the positions of successive posts along at least part ofthe length of the barrier shift relative to the centres of the beamsections.
 2. A road safety barrier according to claim 1, wherein theshift in respect of the posts along part of the length of the barrier isprogressive but uniform.
 3. A road safety barrier according to claim 2,wherein the uniform shift is such as to provide a substantially constantflexibility along that length of the barrier.
 4. A road safety barrieraccording to claim 1, wherein the shift in respect of the posts alongpart of the length of the barrier varies.
 5. A road safety barrieraccording to claim 4, wherein the flexibility of the barrier varies inaccordance with the varying shift along that length of the barrier.
 6. Aroad safety barrier according to claim 1, wherein the spacing betweenadjacent posts along a first section of the barrier differs from that ofa second section, such that the first section has a differentflexibility characteristic from the second section, and that the lengthsof the beam sections forming said first and second sections aresubstantially equal to one another.
 7. A road safety barrier accordingto claim 1, wherein the post spacing is substantially equal along saidat least part of the length of the barrier.
 8. A road safety barrieraccording to claim 1, wherein over a given length of the barrier, theratio of the post spacing to the beam section length or distance betweenadjacent centres lies within the range 0.5 to 1.25.
 9. A road safetybarrier according to claim 1, wherein the beam sections along said atleast part of the length of the barrier are each provided with fixingmeans positioned at more than five locations along their length, thefixing means providing for location and fixing of the posts to the beamsection.
 10. A road safety barrier according to claim 9, wherein saidfixing means of at least some of said beam sections are substantiallyequally spaced apart with respect to one another.
 11. A road safetybarrier according to claim 1, wherein the beam sections are corrugated.12. A road safety barrier according to claim 11, wherein the corrugatedbeam sections have a ‘W’ profile.
 13. A road safety barrier according toclaim 1, wherein at least some of the posts are ‘Z’-shaped incross-section.
 14. A method of constructing a road safety barrier whichat least in part comprises a series of beam sections of substantiallyequal length supported above the ground by posts, the method comprisingshifting the locations of the posts relative to the centres of the beamsections from one beam section to the next.
 15. A method according toclaim 14, wherein the spacing between the posts is substantially equalsuch that said part has a substantially uniform flexibilitycharacteristic.
 16. A method according to claim 14, wherein the spacingbetween the posts progressively varies from one beam section to the nextsuch that the flexibility of the part of the barrier varies along itslength.
 17. A method of testing a crash barrier system, the systemcomprising a series of beam sections together forming a length ofbarrier and supported above the ground by way of posts, wherein thepositions of successive posts along at least part of the length of thebarrier shift relative to the centres of the beam sections such that thestiffness of the barrier varies along the length, the method comprisingconducting road crash tests at differing points along the length anddetermining whether the results of said crash tests satisfypredetermined criteria.